WO2011160748A1 - Preform for producing plastic containers in a stretch blow moulding process and method for producing the preform - Google Patents

Abstract

A preform (1) produced by extrusion blow moulding is proposed, intended for producing plastic containers in a stretch blow moulding process and having a neck portion (4) and a body portion (2) closed by a preform base (3), which portions are separated from each other by a supporting ring (7) protruding from the outer wall. As a difference from the preforms that are known from the prior art, the preform (1) according to the invention has a body portion (2) of which the outside diameter (a) narrows from the supporting ring (7) in the direction of the preform base (3). A method for producing the perform is also proposed.

Description

 Preform for the production of plastic containers in a stretch blow molding process and method for the production of the preform

The invention relates to a preform for the production of plastic containers in a stretch blow molding process according to the preamble of patent claim 1. The invention also relates to a method for producing the preform.

A large number of plastic containers used today, in particular for example plastic bottles and the like, are produced in a stretch blow molding process. In this method, a so-called preform, which usually has a tube-like shape, at its one longitudinal end a bottom and at the other longitudinal end a neck region with molded threaded portions or the like, inserted into a mold cavity of a blow mold and inflated by a blown with overpressure medium. The preform is additionally stretched in the axial direction with a stretching mandrel inserted through the neck opening. After this stretching / blowing process, the finished, stretch-hardened plastic container is removed from the blow mold.

The known preforms are usually produced in an injection molding process. Due to the injection molding process, only relatively low-viscosity materials can be used. The most commonly used raw material for the production of plastic containers in the stretch blow molding process is PET (polyethylene terephthalate). PET has the low viscosity required for the injection molding process at high temperatures around 280 ° C, has been tested many times, and its properties are well known. Unfortunately, PET bottles have very poor barrier properties to water and light, and the incorporation of barrier layers is complex.

For polyolefins, usually PE or PP, processing via the extrusion process without a stretch blow molding process is today the common bottling process.

However, polyolefins do not exhibit optimum stretch hardening in the subsequent stretch blown process. For PET containers to reach the required mechanical strengths (compression pressure, internal pressure resistance, etc.), they should not fall below a minimum wall thickness of approx. 0.2 mm. On the other hand, for ecological reasons and due to the high raw material costs, there is a great interest in further reducing the wall thicknesses of the plastic containers. Preforms for stretch blow molded plastic containers often have a multi-layered structure. For example, preforms having three or more layers are known, including, for example, barrier or getter layers for gases, opaque layers, and so forth. Multilayer preforms are also known in which one or more layers contain regenerated material. In order to bond the different layers to one another, for example, an adhesion promoter is admixed as a blend or as a copolymer to the base polymer or the barrier layer. The adhesion promoter is more or less homogeneously integrated in the raw material or barrier material. Its effect, however, unfolds only at the interfaces of the layers to be joined together. In the rest of the raw material it is of no use and there deteriorates partly the mechanical or barrier properties considerably. For environmental and cost reasons, however, there is an interest in reducing the amount of adhesion promoter. In the production of the preforms in the injection molding process, pressures of up to about 1000 bar usually occur in the melt. In order to keep the required closing forces within reasonable limits, the injection molds often have only a few cavities. This leads for example to preforms with large neck diameters of 48 mm and more for so-called wide-mouth bottles with a relatively small capacity at high production costs.

EP-1 344 618 A1 proposes preforms for use in a stretch blow molding process. The preform, the production of which is not described in more detail, has an outwardly curved shoulder region following the support ring which separates the neck section of the preform from its body section. The inner surface of the preform is formed in the region of the support ring as a conical surface, which widens in the direction of the spherical bottom of the preform. EP-1 344 618 A1 teaches to form the preform with a body portion having significantly larger inner and outer diameters than the neck portion. This known preform is deformed so much during its production that a further and rapid axial and radial orientation in the subsequent stretch blow molding process is too low and does not lead to the desired strain hardening of the produced plastic container.

It is therefore an object of the present invention to provide a preform for processing in a stretch blow molding process, which remedies the described disadvantages of the preforms produced by conventional methods. A preform should be created the one that makes it possible to produce in a stretch blow molding plastic container, which have a sufficient strain hardening. The preform should also allow to reduce the production costs for wide-mouth bottles. Furthermore, the prerequisites for a simple, cost-effective and ecologically acceptable production of multilayer preforms are to be created, which also allow a simple integration of regenerated material.

These objects are achieved according to the invention by a preform for the production of plastic containers in a stretch blow molding process with the features listed in patent claim 1. The objects are also achieved by a method for producing the preform, as defined in the independent method claim. Further developments and advantageous and preferred embodiments of the invention are the subject of the dependent device or method claims. The invention proposes a preform produced by an extrusion blow molding process, which is designed for the production of plastic containers in a stretch blow molding process and has a neck portion and a body portion closed by a preform bottom, which are separated from one another by a support ring projecting from the outer wall. In contrast to the preforms known from the prior art, the preform according to the invention has a body portion whose outer diameter tapers from the support ring in the direction of the preform bottom.

Due to the inventive design of the preform this is deformed during its production by extrusion blowing only to a very small extent. Unlike the known preforms whose body portion is significantly extended in the production by an intense internal pressure, in the production of the preform according to the invention only a relatively small support pressure is required to press the body portion of the preform against the inner wall of the mold, where it is required extent is cooled. An actual radial deformation (elongation) of the body portion is thereby largely avoided. Although the preform is made by extrusion, the classical blowing process does not take place, but only a slight deformation due to the support pressure.

The preforms produced in a quasi-extrusion blow molding process all have the extrusion blow-molding process, but without the disadvantage of only insufficient strain hardening in the subsequent stretch blow-molding process. Alone the transition from the injection molding process to the quasi-extrusion blown process reduces the equipment cost. This is particularly advantageous for the production of preforms with large neck diameters for so-called wide-mouth bottles. Like the injection molding process, the extrusion blow molding process is not limited to the use of low-viscosity raw materials, which are limited in terms of flow through a narrow injection point with high pressure loss. It also allows the processing of higher-viscosity materials whose large macromolecules cause a particularly intense strain hardening. The production of multilayer preforms can be ecologically and economically advantageous, since the extrusion of multi-layer structures is relatively easy to carry out, since they do not have to be passed through an injection point. Instead of having to integrate, for example, a bonding agent in an entire layer, this can be incorporated as an additional layer targeted only in the boundary layer. This significantly reduces the amount of adhesion promoter. Also regenerated material can be integrated very easily during extrusion.

The geometric design of the preform with a body portion which is tapered in relation to the outer diameter of the neck portion ensures that the preform is sufficiently axially and radially stretch-strengthened in the stretch blow-molding process to a sufficient extent. As a result, the plastic container produced has, with the same weight, higher mechanical characteristics, such as compressive compressive strength, internal pressure resistance, etc., as plastic containers which have been produced with preforms of the prior art. This makes it possible to further optimize the inventive preforms in terms of raw cost savings in terms of their wall thickness, without having to make compromises in the mechanical strength of the plastic container produced.

In the two-stage plug-blowing process, the production of the preforms usually takes place temporally and spatially separated from stretch blow molding. In this case, the geometric design of the preform with a body section which is tapered with respect to the outer diameter of the neck section also simplifies the singling and alignment of the preforms usually delivered as bulk material. This takes place for example via two rotating rollers, which are arranged at a distance from each other. The body portions of the preforms fall through the gap between the two rolls. Since the gap width is smaller than the outer diameter measured via the support ring, the preforms are supported via the support ring and can thus be transported to further processing stations. For a particularly good elongation and stretch hardening in the stretch blow molding, the body portion of the preform has an axial length which is about 0.3 times to about 8 times the outer diameter of its neck portion. For example, the preform body has an axial length of about 15 mm to about 150 mm.

For manufacturing reasons, but also for reasons of better strain hardening, it proves to be expedient if the outer diameter of the body portion of the preform continuously tapers in the direction of the preform bottom. In this case, the outer wall of the body portion with the preform axis advantageously includes an angle of 0.5 ° to 5 °.

For the production of plastic bottles with the required mechanical properties, the body portion of the extrusion-blown preform has a wall thickness of 0.4 mm to 4 mm, preferably 1, 8 mm to 2.8 mm.

Depending on the type of plastic container to be produced and intended use of the preform is extruded one or more layers. In this case, the preform has at least one layer of a plastic or of a plastic mixture of the group consisting of polyolefins, polystyrenes, PVC, PVDC, polyester, PLA (polylactic acids) and amides. These raw materials often have large macromolecules, which make them unsuitable for the injection molding process, but on the other hand are very advantageous for the stretch and strain hardening of the plastic container produced by the stretch blow molding from the preform.

In one embodiment variant of the preform, it has at least one layer of PET with an intrinsic viscosity greater than 0.92 dl / g but less than 1.6 dl / g. Another expedient embodiment of the preform provides that it has at least one layer of mono-, bi- or polymodalem HDPE or polypropylene. For example, the preform has at least one layer of HDPE with an MFI 190 ° C 2.16 kg less than 0.1 g / 10 min or MFI 190 ° C 21, 6 kg less than 5 g / 10 min. Another variant of the multilayer preform has at least one layer with barrier additives, in particular oxygen scavengers, light barriers, nanoclays or UV filters. Blocker, up. Alternatively or in addition, the preform may have at least one barrier layer against oxygen and / or UV radiation and / or a lubricious coating and / or a residual emptying coating. The multilayer extruded preform may also have at least one layer of recycled plastic material. The extrusion process also makes it possible to provide the preform at least partially with a different color layer. In this case, a variable color gradient can be set or even a transversely and / or longitudinally striped preform can be produced. A further embodiment variant of the preform provides that it has a transparent viewing strip extending axially in the body section. This can serve as a level control on the finished stretch blown plastic container, for example.

In a further embodiment variant of the preform, it has a neck section with an outer diameter of at least 48 mm. Such preforms are needed for the production of wide-necked containers and can have an outer diameter of up to 300 mm. The extrusion blow molding process for the preforms also allows cost-effective production of such containers. Preform according to one of the preceding claims, characterized in that the outer wall of the neck portion is provided with threaded portions or the like locking projections. The neck portion remains unchanged in the subsequent stretch blow molding process and serves for fastening a screw, snap or bayonet closure or the like.

In contrast to the preforms produced by injection molding or in a flow molding process, in the quasi-extrusion-blown preform, the threaded portions or the like locking projections may be hollow. This saves raw material.

In a further embodiment variant of the preform, the support ring, which separates the neck portion from the body portion, is hollow. The resulting Gewichtsbzw. Raw material saving has an advantageous effect on the production costs of the preforms and thus the plastic containers. In contrast to the extrusion-blown preforms with diameter-sized body sections known from the prior art, the preform according to the invention is hardly radially expanded during production. To form the body portion with an outer diameter, which is tapered in relation to an outer diameter of the Halsab- cut from the support ring in the direction of Preformbodens, the extruded and inserted into the mold cavity hose section is pressed only with a small support pressure against the Forminnenwandungen. Deformation of the preform is largely avoided in this way. A classic blowing process with internal pressures up to 50 bar and higher, as it is known from the usual extrusion blow, does not really take place. The applied for the production of the preform according to the invention support pressure is advantageously only 0.1 bar to 8 bar.

The inventive, quasi-extrusion-blown preforms are for the production of plastic containers, in particular plastic bottles, in a single-stage or two-stage stretch blow molding process. A single-stage stretch blow molding process is understood to mean a process in which the preforms are brought into the final shape immediately after their production. In the two-stage stretch blow molding process, the preforms are separated in time and space from the stretch blow molding process, and the preforms produced are stored until they are used.

Further advantages and embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the single schematic drawing, which shows a not-to-scale representation of an inventive, quasi-extrusion-blown preform in axial section.

The schematically illustrated preform, which bears the reference numeral 1 as a whole, is a preform produced in an extrusion blown process. It has a body portion 2, whose one longitudinal end is closed by a preform bottom 3. The Preformboden 3 can, for example, as shown, have the shape of a spherical surface. In other embodiments of the preforms, the preform floor can also be curved inwards. A further embodiment variant of the preform may be formed with a preform bottom whose inner wall and outer wall bound a flat diverging lens. In conjunction with a suitable refractive index of the preform material of FIGS. 1, 3 to 1, 6, the design of the preform floor as a flat diverging lens means that the electromagnetic heating radiation radiated in to reheat the preform before the actual stretch blow molding process. Radiation is deflected away from the bracket for the preform. This ensures that during reheating a greater proportion of the introduced electromagnetic heat radiation in the preform bottom and in the wall of the body portion is absorbed.

At the opposite end of the preform bottom 3 of the body portion 2, a neck portion 4 adjoins, which is provided with a filling or pouring opening 5. On the outer wall 41 of the neck portion 4 threaded portions 6 or the like projections are formed. The threaded portions 6 or the like projections on the finished stretch blown container allow the screwing or fastening of a provided with corresponding locking elements closure or lid.

The body portion 2 and the neck portion 4 of the preform 1 are separated by a support ring 7, which is also called transfer ring. The support ring 7 protrudes at the transition from the outer wall 41 of the neck portion 4 to an outer wall 21 of the body portion 2 approximately radially.

The body portion 2 tapers from the support ring 7 in the direction of the preform bottom 3. In the illustrated embodiment, the body portion 2 is formed continuously conical. Other embodiments of the preform may, for example, have a body portion which tapers stepwise. A further embodiment variant of the preform may also be provided with a body portion which is curved in the direction of the preform bottom. For example, the body portion has a smaller radius of curvature at the transition to the preform bottom than at the transition to the neck portion.

In the case of the preform 1 shown for example, its body portion 2 has an outer diameter a, which tapers continuously in the direction of the preform bottom 3. In this case, the outer wall 21 of the body section 2 encloses an angle α of 0.5 ° to 5 ° with an axis A of the preform 1. In the case of a stepped body portion which changes its outer diameter, the specified angular range relates to the angle which an imaginary connecting line encloses from the outer diameter of the body portion immediately below the support ring to the outer diameter of the body portion at the transition to the preform bottom with the axis of the preform. The body portion 2 of the preform 1 has an axial length I, which is about 0.3 times to 8 times an outer diameter d of its neck portion 4. The axial length of the body portion 2 of the preform 1 is for example about 15 mm to about 150 mm.

The body portion 2 of the extrusion-blown preform 1 has an average wall thickness w of 0.4 mm to 4 mm, preferably 1, 8 mm to 2.8 mm.

The extrusion-blown preform 1 can be constructed in one or more layers. In this case, the preform 1 at least one layer of a plastic or of a plastic mixture of the group consisting of polyolefins, polystyrenes, PVC, PVDC, polyester, PLA (polylactic acids) and amides. These raw materials usually have large macromolecules, which make them unsuitable for the injection molding process, but on the other hand are very advantageous for the stretch and strain hardening of the plastic container produced by the stretch blow molding from the preform.

A variant of the preform may have at least one layer of PET with an intrinsic viscosity greater than 0.92 dl / g but less than 1.6 dl / g. Another embodiment of the preform has at least one layer of mono-, bi- or polymodalem HDPE or polypropylene. For example, the preform has at least one layer of HDPE with an MFI (melt flow index) 190 ° C 2.16 kg less 0.1 g / 10 min or MFI 190 ° C 21, 6 kg less than 5 g / 10 min.

The preform 1 is made by extrusion blowing. In this case, first a tube is extruded through the annular gap of an extrusion die. The annular gap usually has a gap width of about 0.5 mm to 5 mm. The material is treated very gently during extrusion, as it is extruded "to the outside" and thus no counter-pressure builds up.Injection, however, the material is injected through a needle valve into a Spritzkavität, which has a diameter of about 1, 5 mm to 5 The injection pressures occurring here are from 200 bar to 2000 bar and reach their peak when the injection cavity reaches its maximum level and builds up a high counter-pressure in the mold In this way, deformation of the preform 1 is largely avoided A classic blowing process with internal pressures of up to 50 bar and higher, as known from the conventional extrusion blow-molding process, actually does not take place. The applied for the production of the novel preform 1 support pressure is only about 0.1 bar to 8 bar.

The preform 1 thus produced in a quasi-extrusion blow molding process has in its neck section 4 an inner wall 41 which is recessed groove-like in the region 46 of the threaded sections 6 and in the region 47 of the support ring 7. The production of the preforms 1 according to the invention in a quasi-extrusion blow process enables a gentle treatment of the raw material For example, multilayered preforms which have at least one layer with barrier additives, in particular oxygen scavengers, nanoclays or UV blockers, can be produced very simply Alternatively or in addition to this, preforms with at least one barrier layer against oxygen and / or UV radiation and / or The multilayered extruded preform may also have at least one layer of recycled plastic material The extrusion process also makes it possible to coat the preform at least partially m it to provide a different color layer. In this case, a variable color gradient can be set or even a striped preform can be produced. The preform can be produced with a transparent viewing strip extending axially in the body section. This can then serve as a level control on the finished stretch blown plastic container, for example.

Finally, the production of the preform in a quasi-extrusion blow process also allows a very simple and cost-effective production of preforms for wide-mouth bottles. Such preforms have, for example, a neck portion with an outer diameter of more than 48 mm, preferably 48 mm to 300 mm, measured over the male threaded portions. Because of the high pressures occurring in the injection molding process often only a few cavities can be arranged in the injection molding, otherwise the necessary closing forces are too large. This makes the production of such preforms more expensive. In the quasi-extrusion blow process according to the invention, however, such preforms can be produced comparatively inexpensively. The inventive, quasi-extrusion-blown preforms are for the production of plastic containers, in particular plastic bottles, in a single-stage or two-stage stretch blow molding process. A single-stage stretch blow molding process is understood to mean a process in which the preforms are brought into the final shape immediately after their production. In the two-stage stretch blow molding process, the preforms are separated in time and space from the stretch blow molding process, and the preforms produced are stored until they are used.

Claims

Preform for the production of plastic containers in a stretch blow molding process, which has a neck portion (4) and a body portion (2) connected to it with a preform bottom (3) and projecting through a support ring projecting from the outer wall of the preform (1) (7) are separated from each other, characterized in that the preform is produced in an extrusion blow process and the body portion (2) has an outer diameter (a) which is tapered from the support ring (7) in the direction of the preform bottom (3). Preform according to claim 1, characterized in that the body portion (2) of the preform (1) has an axial length (I) which is about 0.3 times to about 8 times an outer diameter (d) of its neck portion (4). is. Preform according to claim 1 or 2, characterized in that the outer diameter (a) of the body portion (2) continuously tapers in the direction of the preform bottom (3). Preform according to claim 3, characterized in that the outer wall (21) of the body portion (2) with the preform axis (A) encloses an angle (a) of 0.5 ° to 5 °. Preform according to one of the preceding claims, characterized in that the body portion (2) has an average wall thickness (w) of 0.4 mm to 4 mm, preferably 1, 8 mm to 2.8 mm. Preform according to one of the preceding claims, characterized in that it is extruded one or more layers. Preform according to one of the preceding claims, characterized in that at least one layer of a plastic or of a Kunststoffge- mixed of the group consisting of polyolefins, polystyrenes, PVC, PVDC, polyester, PLA and amides. 8. preform according to claim 7, characterized in that it comprises at least one layer of PET having an intrinsic viscosity greater than 0.92 dl / g but less than 1, 6dl / g. 9. preform according to claim 7, characterized in that it comprises at least one layer of mono-, bi- or polymodalem HDPE or polypropylene. 10. preform according to claim 9, characterized in that it comprises at least one layer of HDPE with a MFI 190 ° C 2.16 kg less than 0.1 g / 10 min or MFI 190 ° C 21, 6 kg less than 5 g / 10 min. 1 1. A preform according to any one of claims 6 to 10, characterized in that it is extruded multi-layered and at least one layer with barrier additives, in particular oxygen scavengers, nanoclays or UV blockers having. 12. Preform according to one of claims 6 to 1 1, characterized in that it is extruded multi-layered and has a barrier layer against oxygen and / or UV radiation and / or a lubricious coating and / or a residual emptying coating. 13. Preform according to one of claims 6 to 12, characterized in that it is extruded multi-layered and has at least one layer of recycled plastic material. 14. Preform according to one of the preceding claims, characterized in that it has a in the body portion (2) axially extending transparent viewing strip. 15. Preform according to one of the preceding claims, characterized in that the outer wall (41) of the neck portion (4) is provided with threaded portions (6) or the like locking projections. 16. Preform according to claim 15, characterized in that its neck portion (4) has an outer diameter measured via the threaded portions or the like, which has at least 48 mm and up to 300mm. 17. Preform according to claim 15 or 16, characterized in that the threaded portions (6) or the like locking projections are hollow. 18. Preform according to one of the preceding claims, characterized in that the support ring (7) is hollow. 19. A method for producing a preform according to one of the preceding claims, wherein a single- or multi-layer plastic tube extruded and according to the mold cavity of a blow mold to a preform (1) with a neck portion (4) and an adjoining, with a Preformboden (3 ) closed body portion (2), which are separated by a projecting from the outer wall of the preform support ring (7), is formed and demolded, characterized in that the enclosed by the mold cavity plastic tube for forming the body portion with an outer diameter, the is tapered from the support ring in the direction of the Preformbodens is pressed with a support pressure against the Forminnenwandungen. 20. The method according to claim 19, characterized in that the support pressure is 0, 1 bar to 8 bar. 21. Use of an extrusion-blown preform (1) according to one of the claims 1 to 18 for producing a plastic container, in particular a plastic bottle, in a one-stage or two-stage stretch blow molding process.